A vacuum tube, an electron tube, or just a tube (USA), or valve (GB) is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a heated cathode.

A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers during the 1960s and 1970s.

Valve amplifiers are used for applications such as guitar amplifiers, audiophile stereo amplifiers, military applications and very high power radio and UHF television transmitters.